1. Field of the Invention
The invention relates to accumulator (common rail) type fuel injection apparatuses, and internal combustion engines provided with those pressure accumulation-type fuel injection devices, that are furnished with an accumulator pipe (also known as “common rail”) that is employed in the fuel supply system of an internal combustion engine (such as diesel engines). In particular, the invention relates to measures for appropriately obtaining the injection amount of the fuel that is to be supplied from the injectors to the combustion chamber.
2. Description of the Related Art
In the past, pressure accumulation-type fuel injection devices, which have superior controllability compared to mechanical fuel injection pump-nozzle apparatuses, have been proposed for the fuel supply system of a multi-cylinder diesel engine (for example, see Patent Documents 1 and 2 listed below).
Such fuel injection apparatuses store, in a common rail, fuel that has been pressurized to a predetermined pressure by a high-pressure pump, and the fuel that is stored in the common rail is injected into the combustion chamber from a predetermined injector in accordance with the fuel ejection timing. A controller performs calculations to control the fuel pressure within the common rail (hereinafter, called the common rail pressure) and the injectors so that fuel is injected under the most ideal injection conditions for the operating state of the engine.
Thus, in pressure accumulation-type fuel injection devices it is possible to control not only the fuel injection amount and the injection timing, but also the fuel injection pressure, which is determined by the common rail pressure, according to the operating state of the engine, and thus pressure accumulation-type fuel injection devices have gained attention as injection apparatuses that possess excellent control characteristics. In particular, such pressure accumulation-type fuel injection devices have favorable pressure increase properties in the low revolution speed region of the engine and this allows high-pressure fuel injection to be performed from the low speed region, and therefore the fuel can be atomized over all regions. For this reason as well, pressure accumulation-type fuel injection devices have garnered interest from the standpoint that they can significantly reduce the black smoke that is characteristic of diesel engines.
—Schematic Structure of the Pressure Accumulation-Type Fuel Injection Device—
A general pressure accumulation-type fuel injection device is described below.
FIG. 13 schematically shows the overall configuration of the fuel supply system of a multi-cylinder diesel engine provided with a pressure accumulation-type fuel injection device. This pressure accumulation-type fuel injection device is provided with a plurality of fuel injection valves (hereinafter, referred to simply as injectors) b1 each of which is attached to a cylinder of a diesel engine (hereinafter, referred to simply as an engine) a, a common rail c that accumulates high-pressure fuel that is at relatively high pressure (common rail pressure: 100 MPa, for example), a high-pressure pump (supply pump) f that pressurizes the fuel that is sucked from a fuel tank d by a low-pressure pump e to a high pressure and then ejects it into the common rail c, and a controller (ECU) g for electrically controlling the injectors b and the high-pressure pump f.
Each injector b is attached to the downstream end of a fuel pipe each of which is in communication with the common rail c. The injection of fuel from each injector b is controlled by supplying and cutting off electricity (ON/OFF) to an injection control solenoid valve h that is provided in an intermediate portion of the fuel pipe. That is, the injector b injects the high-pressure fuel that has been supplied from the common rail c toward the combustion chamber of the engine a while its injection control solenoid valve h is open. Thus, it is necessary for the common rail c to accumulate a high predetermined common rail pressure that corresponds to the fuel injection pressure, and thus the common rail c is connected to the high-pressure pump f via a fuel supply pipe i and an ejection valve j.
The ECU g is supplied with various types of engine information such as the engine revolution and the engine load, and outputs a control signal to the injection control solenoid valve h so as to obtain the most suitable fuel injection timing and fuel injection amount, which are determined from these signals. At the same time, the ECU g outputs a control signal to the high-pressure pump f so that the fuel injection pressure becomes an ideal value for the engine revolution or the engine load. Further, a pressure sensor k for detecting the common rail pressure is attached to the common rail c, and the fuel ejection amount that the high-pressure pump f ejects to the common rail c is controlled so that the signal of the pressure sensor k becomes a preset ideal value according to the engine revolution or engine load.
—Method for Calculating the Fuel Injection Timing and the Fuel Injection Duration—
Next, a conventional example of a method for calculating the fuel injection timing and the fuel injection duration with the ECU g is described. FIG. 14 shows the change in the crank signal, the electricity conduction signal to the injection control solenoid valve h, and the common rail pressure, at a timing when fuel is injected from a particular injector b. Here, the crank signal is a pulsed waveform that is transmitted every 6° of rotation of the crank. The operation of injecting fuel from the injector b is executed while the electricity conduction signal to the injection control solenoid valve h is ON.
First, the ECU g calculates the fuel injection start timing based on various types of engine information such as the engine revolution and the engine load. FIG. 14 shows a case in which fuel injection is started at the timing B by starting the supply of electricity to the injection control solenoid valve h.
The fuel injection duration, on the other hand, is calculated by the ECU g based on the fuel injection amount that has been determined and the common rail pressure so as to attain the engine revolution (target revolution) that corresponds to the opening signal that the ECU g receives from the throttle (regulator in marine engines). The injector b continues the fuel injection operation based on the common rail pressure so as to attain the determined fuel injection amount, and the engine revolution in this state is detected and compared to the target revolution, and the fuel injection amount is corrected so that the actual engine revolution approaches the target revolution (feedback correction).
To describe this in further detail, the ECU g determines the fuel injection amount before the timing B (the time when the supply of electricity to the injection control solenoid valve h is started) so as to obtain the engine revolution (target revolution) according to the opening signal of the throttle (regulator in marine engines). Then, the fuel injection duration (this corresponds to the time during which electricity is conducted to the injection control solenoid valve h; the time from the start of fuel injection to the end of fuel injection) is calculated according to the common rail pressure when the crank signal (pulsed waveform) rises (timing A in FIG. 14) before the timing B, and the fuel injection amount that has been determined as above. In FIG. 14, Tdur is found as the fuel injection duration and indicates the timing C at which point the supply of electricity to the injection control solenoid valve h is interrupted to cease fuel injection.
The fuel injection timing and the fuel injection duration thus are found through the above operation.    Patent Document 1: JP 2000-18052A    Patent Document 2: JP 2003-328830A